1. Field of the Invention
This invention relates to an ink jet printer and an ink jet recording unit for jetting ink for recording.
2. Description of the Related Art
In recent years, machines using an ink jet recording method have spread over a wide range, and a large number of ink jet recording units enabling a recording head and an ink tank to be separated have been introduced on the market. Many actual commercial products may have an ink tank and a recording head unit detachable for replacement. In the machines having a replaceable ink tank, when the ink tank is replaced, bubbles are easily mixed into a recording head and it is feared that ink will not be jetted from the recording head.
An ink jet recording unit having a replaceable ink tank is formed with corners projected in the surroundings of a flow passage for supplying ink to a recording head so as to supply ink from the corners, for example, as described in Japanese Patent Laid-Open No. Hei 4-250046.
However, in this structure, the corners are formed in the surroundings of the flow passage which is circular in cross section. Thus, for example, if the flow passage is placed in three dimensions, it is difficult to couple the corners to the flow passage and it is hard to manufacture the structure.
The corners are shaped like fine slits as compared with the flow passage circular in cross section. Thus, if the flow passage circular in cross section has a large diameter, corners can also be formed, but if the flow passage circular in cross section has a small diameter, corners becomes hard to form.
As described later, if a structure wherein the cross-sectional area of a flow passage is changed gradually is adopted, slit-like corners become extremely thin; it is feared that a capillary force hinders an ink flow, causing an excessive pressure loss, making it impossible to jet ink.
Considering miniaturization, it is desirable that the pipe diameter of the flow passage is thin, of course. However, if it is too thin, it is easily predicted that the flow rate of ink will increase at the ink supply time in a print state, causing bubbles to flow.